300 University of California Publications in Zoology [Vol. 23 



all the specimens were very much undersized. Together with Crago 

 mgricauda and C. franciscorum this species is one of the only three 

 that were taken at more than three stations in the upper bay, and 

 together with these two and Hemigrapsus oregonensis is one of the 

 only four taken at any of the upper bay stations lying north of Pinole 

 Point. 



In general salinity seems to be the controlling factor in the 

 separation of the strictly outside species from those found in or "in 

 and out" of the bay, and character of bottom that in the distribution 

 of species within the bay. Though so important geographically, the 

 effect of temperature on the local distribution of species is not at all 

 evident. Depth, likewise, apparently exerts little or no influence 

 on the distribution of the survey species : certain species were taken 

 only beyond the 30 fathom line and others only in the course of shore 

 collecting, but the relation of the former to the salinity outside, and 

 the latter to their substratum is too intimate to permit any other 

 explanation. That only four decapods are known to occur in the 

 upper bay north of Pinole Point is probably due to the low salinity 

 there obtaining, for although the annual range of temperature in this 

 division is considerable it is almost equally great in the more populous 

 but much more saline lower bay. 



